The invention relates to the materials handling sector and the continuous transport of materials by conveyor belts, and in particular to conveyor belts which are formed into a trough and supported by flexible elastic rollers.
The Applicant is the owner of European patent 506 036 (corresponding to U.S. Pat. No. 5,248,029, the disclosure of which is incorporated by reference herein in its entirety) which relates to an automatic centering device for this type of conveyor belt which is satisfactorily marketed under license according to a regular development that validates and justifies the technical choices in the said European patent.
In order to facilitate understanding of the invention in the present improvement, specific reference is made to the original invention as shown in FIGS. 1, 2 and 3 attached.
More particularly, according to the said European patent the automatic centering device for flexible conveyor belts is supported by two rows of flexible rollers (4) comprising a single central fastening (9) providing a positive toe-in angle which recalls the trough-shaped belt to a stable dynamic equilibrium on the axis of the conveyor.
The single central fastening (9) which is located lower than the external roller fastening points (5) and is common to each pair of said flexible rollers (4) is movable and, when its altitude varies with the load, it has a curved trajectory matching the longitudinal trajectory of the belt imposed on it by the rotation of the swinging lever (10) supporting the single movable central fastening around the stationary pin (12) so as to reduce the toe-in angle according to the load carried.
The trajectory of the central fastening rotating around the fixed pin is adjusted so that the toe-in is cancelled out for the maximum value of the load transported.
A conveyor belt implementing the aforementioned automatic centering devices uses several strings disposed in alignment on the trajectory in question to ensure transport and handling of the load.
To this end the central fastenings (9) of several flexible supports are connected to one another by their respective levers attached to a tensioning cable. The stationary pin (12) of each of the said levers is connected to an attach tab (6) fastened to said cable disposed along the longitudinal axis (13) of the tensioned conveyor between an adjusting screw (15) and tensioning means (16) that are themselves fastened to the conveyor chassis.
The conveyor belts described that implement the conveyor belt automatic centering device are marketed under the trade mark xe2x80x9cValrolxe2x80x9d in France and xe2x80x9cWackemxe2x80x9d in Italy and Spain.
On a conveyor belt the carrying run is subject to load variations due to variations in the rate of materials being transported while the return run of the conveyor belt is subject to the same load variations under certain specific circumstances:
where the conveyor belt also carries materials on its return run; in this case it is subject to the same treatment as the carrying run;
where in certain zones of the conveyor belt, convex segments (centre down) or curves on the horizontal plane, the variations in the rate cause variations in the tensions in the belt and hence variations in the load on all the strings of rollers in the zone in question, hence desirable variations in the toe-in angle of the rollers forming the said strings.
The embodiment of patent EP 504 036 with, in particular, the central cable and the associated tensioning devices together with the swinging lever and the attach tabs fastened to the cable have their use on both the carrying run and the return run.
Even though this embodiment is perfectly satisfactory, the Applicant""s approach is to try to further improve the operation and standardisation of the conveyor belt automatic centring device and the components associated therewith.
This approach has resulted from various findings.
Firstly, the single central fastening (9) described in EP 504 036 incorporates an integral V-shaped shaft (11) on which are fastened two rollers (4).
This single central fastening, the height of which varies according to the load being carried, supports the swinging lever (10) that rotates around stationary pin (12) allowing adjustment of the toe-in angle under no-load conditions and reduction of the said toe-in when the load increases.
This single central fastening can have several drawbacks that nevertheless do not undermine the basic concept of the main invention.
Firstly, the angle formed between the V-shaped shaft (11) and the horizontal axis is constant irrespective of the curve of the assembly created by the single central component (9) and the two rows of elastic rollers (4).
This single central component requires fitting of the two rollers on the V-shaped shaft thereby creating an assembly that is fastened to the shaft. This means that the swinging lever cannot be removed and the entire single central component has to be removed even if only one component thereof is worn.
This situation may cause problems as the central fastening is the fastening most subject to stress and it is sometimes necessary to replace it with spare parts.
It will easily be understood that if one of the rollers is worn, having to replace the central fastening assembly greatly increases the cost of repair and replacement.
A further drawback lies in the fact that the said single central fastening included in embodiments of the concept disclosed in EP 504 036, by reason of its V-shaped shaft, requires special packing for storage and delivery operations. This is due to the non-linear nature of the string formed by the central component, the two rows of elastic rollers and the end-fastenings.
The Applicant""s approach has therefore been to take these findings and examine how it is possible to optimise the general concept patented in EP 504 036 in order to reduce the repair costs, facilitate changing the rollers when worn and also bring greater elasticity to the central fastening assembly, particularly the rollers which, even when adjacent do not necessarily bear the same load.
The Applicant""s approach has therefore been to optimise this fastening system.
The Applicant""s approach has also been to rationalise and standardise the various components that can be used in this fastening concept on both the carrying run and return run of the conveyor belt wherever variations in the load carried or the tensions due to variations in the rate require changes of toe-in angle.
All these factors have caused the Applicant to find a technical solution that does not threaten the correct operation of the concept patented in EP 504 036 but which also offers improvements and substantial gains in productivity when using embodiments of the present invention.
These goals and others will become clear from the rest of the description.
According to a first aspect of the invention, the improved automatic centering device for a conveyor belt supported by a string of elastic rollers in which the toe-in angle varies according to the load carried, the device being of a type including a central fastening that receives rollers oriented in a V configuration between which is disposed a swinging lever that is subject to a movement in a trajectory that curves according to the variation in altitude due to the load on the conveyor belt, the lower end of the said lever operating in conjunction with an attach tab fastened to an adjustable tensioning cable relative to the bearing chassis of the conveyor belt, the central fastening rollers being mounted so they are free to rotate on their independent axles oriented in a V configuration, the said axles being fastened to but removable from an opposite end, at a given angle, by central fastening means, said central fastening means being fastened to an attach tab designed to receive so that it may be dismantled and so that it pivots, the swinging lever, the other end of which is fastened to the attach tab fastened to the tensioning cable.
These aspects and others will be understood from the rest of the description.